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I´m using water container placed on a radiator to humidify room air. Someone might argue that it is a perfect nest for bacteria. I have to put copper coins into the water to kill the bacteria.

I would like to do an experiment, have two similair containers filled with water one with copper coins, the other without them.

I would like to compare how many bacteria are living in those containers, how can I do that? (in home conditions)

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4 Answers 4

There is evidence that copper pots have antibacterial effects when used for storing drinking water (Sudha, et al. 2012), so the copper coins will probably have a similar effect.

The easiest way to test this at home would probably be to buy a test kit from an online vendor - these are relatively inexpensive.

Some Googling produced this website [appslabs.com.au], which has some tests for common types of bacteria. There are undoubtedly others too, if these don't sound suitable

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Anything I can get in Europe? Do you have any recommendation on type/brand? –  Hurda Oct 20 '13 at 20:54
@Hurda I'm afraid not - I've not used them myself, just found them by searching on the internet. Find one with some good reviews! –  Luke Oct 20 '13 at 21:52

I think you might be better advised to try plating out samples of the water and counting bacterial colonies. There has been some good advice on doing basic microbiology at home elsewhere on this site.

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I don't understand how this should help me to determine, which sample (container) conatined more bacteria before I started cultivation (and put any number to that)? Is it the speed at which the cultivation progress? –  Hurda Oct 20 '13 at 20:57
Thanks to leonardo for answering this before I got a chance to! –  Alan Boyd Oct 21 '13 at 13:41

I would first like to address a couple of your underlying assumptions:

1) Most "copper" looking coins (in North America anyway) are actually a bronze alloy, reflecting a change from ~95% Cu to ~95% steel. As a result, I don't think that there would be much antimicrobial effect from the coins. Now, if you did really have copper in the water (like copper piping), then the best antimicrobial effects are likely to come from regular stirring/agitation to make sure the bacteria contact the copper.

2) Having some tap water sitting in a warm area is not really a "perfect" breeding ground for bacteria. A perfect breeding ground would contain nutrients (at the very least, sugar). Whatever bacteria you would find is likely the bacteria that circulates in your home air, or other contaminants (like sneezing).

As for your question, how to measure the bacterial load in each bowl, I think the simplest method to do at home would be as @Alan Boyd suggests. Take a small sample of water from each dish, and plate them out on some kind of growth plate (such as a LB agar). After 16-18 hours of growth on the plate, you would just count the number of colonies on each plate, and get a simple measurement of bacterial load from each bowl.

The drawback to this method is that it does not tell you what kind of bacteria are growing, or whether they are likely to cause illness (pathogenic).


For reference, here is a detailed overview of the most common types of agar plates used for microbiology purposes. This is also a protocol for how to make your own plates at home, using readily available gelatin as a gelling agent, rather than using agar (which can be found in some ethnic supermarkets, but is less available).

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It,s Euro cents, they claim copper coating of Fe body. I'm trying to measure the antibacterial effect (instead of just assuming something) - compared to no additive and based on suggestion also real copper (old GPU heatsink) –  Hurda Oct 21 '13 at 12:41
Sounds good, I was just pointing out a few things for you to consider. –  leonardo Oct 21 '13 at 17:30
@Hurda, I added two references for commonly used agar plates, as well as a method to make your own plates at home with readily available home ingredients. –  leonardo Oct 22 '13 at 1:37

I have no idea, how your containers look like [and I doubt that's the best way to humidify air] and I don't think there is any chance to get rid of bacteria by putting some copper coins inside, but any-case:

The easiest way to measure concentration of bacteria utilized in laboratory practice is with the aid of a spectrophotometer. There are lots of protocols on-line, but basically you need a spectrophotometer able to measure absorption at 600 nm, special cuvettes and pipettes. One major drawback is that this way you get relative amounts of bacteria, and to get an idea, of how much cells in one unit of volume you actually have, you need calibration. [Calibration curves are unfortunately not transferable from photometer to photometer or from one bacterial culture to another one]. Calibration is generally performed by measuring absorption of media with different a priori known concentrations of bacteria. To get such control media, one needs a more laborious trick: measure individual cells from a known volume under a microscope (pour, say 1 mkl of the medium on a glass and "just" count all cells).

Moreover, you likely need a centrifuge, capable of rotating at 5000 g, because bacterial content in your water is not going to be high enough and you have to collect the cells and re-suspend them later in much smaller volume.

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Few homes have a spectrophotometer, so this is not suitable approach "in home conditions" as was asked for. –  mgkrebbs Oct 21 '13 at 17:54
Yes, perfect reason for a down-vote. I wrote: "in laboratory practice". E.g., I also don't have LB in my kitchen or a thermostate. –  har-wradim Oct 21 '13 at 18:38

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